New gun for CRT

[LENINGRAD T2]

The used cathode changes its properties when removed from the CRT. There is little chance that it will work when the vacuum is re-created. There is also another problem. The new electron guns were delivered with a suction tube for connection to a vacuum pump as a ready set to be embedded in the neck of the picture tube. If we try to integrate a used electron gun, we have no way of connecting a vacuum pump. It would be necessary to melt the suction tube. This complicates the whole process a lot.

[AdrianPH]

OK so when a cathode has been activated then I can understand it may not like being exposed to air, I watched one of the youtube videos by glasslinger, I was sure it was mentioned taking a heater and cathode from a valve to re-use, perhaps it was just a heater?

On re-using the gun assembly I wonder about cutting off on the spot welds to the pins and re spot welding to a glass base with pins and evacuation tube. For some tubes rebuilding as per Jeffrey's post 6 may be the only solution if a new cathode and heater can be sourced.

Is the Brimar project still active and have they any plans to produce CRT guns, or suitable parts for them?

Adrian

[ppppenguin]

CRT HK assemblies are different to those used in valves. I have no idea if new CRT HK assemblies are available or how difficult they would be to make.

Cathodes are activated after the CRT is pumped. The emissive surface is ruined by exposure to air.

For normal CRT regunning, the neck is cut and a new gun assembly fused to the old neck. It is possible to fuse a new "pinch" (the term used for the piece of glass that has the metal-glass seals for the leadouts and also the pumping stem) to the existing glassware. Modern pinches are probably available.

If the CRT is Pyrex (this is mainly for prewar CRTs) you can't attach soft glass parts directly. This would apply, for example, to a mdoern pinch. The differing coefficients of expansion would crack the joint. The solution is a graded seal, with 2 or 3 different special intermediate grades of glass. This requires a high level of glassblowing skill.

My 1987 article: https://www.borinsky.co.uk/vintage_tube.html covers some of this, though in a rather lighthearted way.

PS: I saw a reminder today that Thomas Electronics are still in the CRT business: https://www.thomaselectronics.com/faq/
http://videokarma.org/showthread.php?t=274039
I think I approached them a few years ago and got nowhere.

[LENINGRAD T2]

What I am going to say is a cliche, but I would like to emphasize once again that replacing an electron gun in a CRT is a very difficult task. New cathodes are needed that no one produces. The workshop I wrote about has such elements and different types with pumping tubes. It is probably a phenomenon on a global scale. As a result, it is possible to regenerate various types of picture tubes irrespective of their electrical structure. Melting glass takes a lot of skill, and I don't think anyone will get it right with a CRT after a few tries in the garage. I think that the only thing that is unlikely to be a problem today is to create a vacuum. According to the original method, the picture tube had to be heated to about 400 degrees during pumping. Today, this stage can be omitted by using better-quality pumps, e.g. turbomolecular pumps. Of course, the final product must be safe. It can't break in your hands.

I am eager to join the project of regenerating a damaged pre-war picture tube. Unfortunately, I do not have one, and no one sells such old CRT on well-known auction sites.